Conversion of hydrocarbon gases to hydrogen and carbon monoxide



May 1, 1951 M 1 7 n o e 5 m 5, b 2 n e h s 2 A. B. WELTY, JR CONVERSION 0F HYDROCARBON GASES TO n HYDROGEN ANI)` CARBON MONOXIDE Filed June 28, 1946 Tfm a@ mb dmEQxOmd,

mm uji.

ZmOOdZ d liberi Uelyfr,

:5x-:Alentour May l, 195l A. B. WELTY, .JR 2,550,742

- CONVERSION OF HYDROCARBON GASES TO HYDROGEN AND CARBON MONOXI'DE Filed June 28, 3.946 2 Sheets-Sheet 2 NATURAL. GAS

omos

'y Clbbcr'nen Patented May l, 1951` CONVERSION OF HYDROCARBON GASES TO HYDROGEN AND CARBON MONOXIDE Albert B. Welty, J r., Mountainside, N. J., assigner to Standard Oil Development Company, a corporation of Delaware Application June 28, 1946, Serial No. 679,886

Claims. (Cl. 48-196) The present invention relates to the conversion of hydrocarbon gases. More specifically, the invention is concerned with the conversion of hydrocarbon gases such as natural gas, methane, ethane, or the like to form'gas mixtures containing carbon monoxide and hydrogen, and particularly such gas mixtures as are useful as feed gas for the catalytic synthesis of' hydrocarbons and/or oxygenated organic compounds.

It is well known in the art that gaseous hydrocarbons such as methane may be oxidized to form gas mixtures containing carbon monoxide and hydrogen. While air may be used as the oxidizing agent in this reaction the resulting dilution of the product gases with nitrogen has prompted various proposals and attempts to use pure oxygen or metallic oxides to supply the oxygen required for the oxidation of the hydrocarbon gas.

The use of pure oxygen requires expensive air fractionation equipment. When the oxidation is carried out by passing the hydrocarbon gases over suitable metal oxides, the extent of the reaction is diicult to control as a resultfof the excess of oxygen which is available for reacting with the incoming feed.

Some of these difficulties may be alleviated by reacting controlled amounts of nely divided metal oxides with a specific volume of gaseous hydrocarbons to be oxidized in a reaction zone at controlled reaction conditions. However, the for-- mation of CO2 and steam as oxidation products cannot be completely avoided and it has been found desirable to combine this oxidation process with a so-called reformation reaction wherein CO2 and/or steam are reacted with unconverted or fresh hydrocarbon gas in the presencey of a so-called reformer catalyst such as nickel, nickel supported on alumina or magnesia, or the like to form additional amounts of CO and H2.

It is theoretically possible and has been suggested to carry out the oxidation and reformation vreaction in a single reactor using the socalled fluid solids technique in which a mixture of finely divided metal oxide and reformer catalyst is admixed with the hydrocarbon gases to form a dense turbulent suspension resembling a boiling liquid with respect to hydrodynamic and hydrostatic properties. The metal oxide is reduced in the course of this reaction and must be reoxidized continuously or at intervals in order to maintain the desired oxygenrconcentration in the reactor. This reoxidation may be accomplished by withdrawing reduced metal oxide from the reactor, reoxidizing it with air in a separate vessel and returning it to the reactor.

However, this procedure involves a similar treatment of the reformer catalyst which is intimately mixed with the metal oxide to be reoxidized, and I have found that the reformer catalyst loses in activity when subjected to oxidation in the metal reoxidation zone, which is diicult to avoid when fluidized mixtures of metal oxide and reformer catalyst are used in the process.

'I'he present invention overcomes these diiculties and affords various additional advantages, as will appear from the following description thereof read with reference to the accompanying drawing which shows semi-diagrammatic views of apparatus adapted to carry out preferred embodiments of the invention.

It is therefore, a principal object of the present invention to provide an improved process for the conversion of gaseous hydrocarbons into gas mixtures containing carbon monoxide and hydrogen.

Another object of this invention is to provide an improved process for converting hydrocarbon gases into gas mixtures containing carbon monoxide and hydrogen by oxidation and reformation using the fluid solids technique.

A more specific object of the invention is to provide a process of the type specified which affords improved yields of a gas mixture suitable as a feed gas for the catalytic synthesis of hydrocarbons and/or oxygenated organic compounds.

A still further object of the invention is to provide an improved process of the type ,specified wherein oxidation and reformation may be conducted simultaneously in a single uid conversion zone.

Other and further objects and advantages will appear hereinafter.

In accordance with the present invention substantially complete conversion of gaseous hydrocarbons such as methane, ethane, natural gas, or the like into mixtures of carbon monoxide and hydrogen suitable for the hydrocarbon synthesis, may be effected by contacting the gaseous starting material with a uidized mixture of finely divided metal oxide and reformer catalyst, effecting a separation of reduced metal oxide from reformer catalyst, reoxidizing the reduced metal oxide with an oxidizing gas in the absence of a substantial proportion of the reformer1 catalyst, mixing the reoxidized metal oxide with the separated reformer catalyst and using this mixture for the conversion of further amounts of hydrocarbon gases into carbon monoxide and hydrogen;

neighborhood of about 5.0. Thisfdiierencefhas been found sufficient to make a separation by density feasible to a practical degree'.4

In accordance with the preferred:v embodimentof my invention, therefore, I withdraw a fluidized mixture of relatively heavy reduced-v metal oxide and relatively light reformer catalyst from the gas conversion zone, effect at least a crudesep'-V aration of relatively heavy from relatively light solid particles,n subject the relatively heavy `particles to reoxidation' andfreturn both 'theun oxidized relatively light' and thefreoxidized" relatively' heavy particles to the iiuidized mixture of solids in the conversion zone.

I have found' that the centrifugal force'fdevelope'd by a relatively sudden change inv the direction" of flow ofv the luid'ized mixture kof solids owing through any forced path at arela'- tivelyv high velocity is sufficient to accomplish the desired degree of separation between reduced metal oxide and refornfier catalyst of` substantially lower' specific gravity; A- directional change of this typeV is my preferred means'o'f causing the desired separation by density as will appear more clearly hereinafter.

Having set forth its objects and general natu-re, the invention willbe bestunderstood from the more detailedl description hereinafter, in which reference will be made to the accompanying drawing whereinY Figure lis a diagrammatic Viewof a` system suitable for carrying out theconversion of hydrocarbon gases iny accordance Withmy invention; and

Figure 2 illustrates diagrammatically my preferred means of separating reducedmeta'l oxide from reformer catalyst.- l

Referring now in detailto Figurehthe system illustrated essentially comprises a hydrocarbon gas converter l!) and a metal oxide reoxidizer 5o; both adapted to iiuid solids operation and cooperating as will be presently explained.

In operation, converter I0 whichL may be provided with a foraminous distributionplate such as a grid 3 is supplied through line l with a mixture of nely divided-metal oxider and reformer catalyst. While certain oxides which. are reduced to metals by the hydrocarbonY gases, such as ferrous oxide, cuprous oxide, and the like, are useful for my process other suitable oxides are the higher oxides of metals which are capable of forming both higher and lower oxides.; such as c'upric oxide,rvanadium pentoxide, ferrie oxide, stannic oxide, and others. The reformer catalyst preferably comprises nickel as its active component supported on such carriers as alumina, magnesia, kaoline, etc. in concentration of Y about 2-40% by weight of total catalyst. The relative amounts of metal oxide and reformer catalyst may vary within Wide limits depending on the specific materials used and the course ofi reaction desired. In general, good results are obtained with solids mixtures'containing about -70%, preferably about 25.45%' by 4 weight of reformer carrier catalyst and about 30-90% preferably about 65-'75% by weight of metal oxide such as ferric oxide or cupric oxide. The particle size of the solids should be within the fluidizable range of about 50-400 mesh preferably about -350 mesh. If desired, different particle sizes may be chosen for the metal oxide and the reformer catalyst in order to assist in the subsequent separation of these solids and/or to accomplish a rough classiiication within the fluidized beds of converter it and reoxidizer 5&1.

A. hydrocarbon'gas, such as natural gas, is supplied through line 5 and enters converter il) through grid 3 at an upward flow velocity adequate toA form above grid 3 a uidized dense turbulent' mass of solids having a well dened upper level 'll linear gas velocities of about 0.3-4, preferably 0.75-3 ft. per second, depending on the particle size of the solids, and space velocities of about 3-30 preferably about 5-10 cu. ft. of gas (measured at standard conditions) per lb. of solids in converter l0 per hour, are' generally suitable for this purpose. The temperature within converter! t is maintained within the approximate limits of 140018G0 F., preferably '1500"- 1700" F., at which a substantial proportion of the methane of the natural gas isoxidized by the metal oxide to form CO, CO2, H2' and water, and CO2 and water' are reacted with unoxidized methane to form additional amounts of CO and En. The net heat etect of this reaction' is slightly endothermic and heat must be supplied to maintain the temperature at the desired level. This is preferably accomplished by supplying heat in the form of sensible heat of metal oxide returned from reoxidizer 50, as will appear more clearly hereinafter. The pressure within converter I0 may be subatmospheric,Y atmospheric, or superatmospheric, elevated pressures varying between about '75400' lbs. per sq. in, being preferred for the production of feed gas for the hydrocarbon synthesis.

Product gas comprising carbon monoxide and hydrogen in the approximate ratio of 0.3-2 volumes of carbon monoxide per Volume oi' hydrogen is taken overhead from. converter lll through line I2. If desired, the product gas may be freed of entrained solids fines by conventional mechanical and/or electrical` gas-VA solids separation means (not shown) from which separated solids may be returned to converter ID in a manner known per se.

A fluidized mixture of reduced metal oxide and reformer catalyst is withdrawn downwardly from converter I0 through a substantially vertical standpipe 2t] provided with slideA valve 25. The lower portion of standpipe 2e is curved at 30 and leads into a substantially Vhorizontal pipe 32. The uidized solids mixture which may be further aerated with a fluidizing gas supplied through taps 23, iiows downstandpipe 20 at a relatively high velocity controlled by slide valve 25. The velocity below slide valve 25 may be further increased by the injection into standpipe 2] of small amounts of steam or other inert gas supplied through line 28. Linear velocities of about 30 to 100 ft. per second in the lower portion of standpipe 2i] are generally suitable for my process. The radius of curvature at the bend may be 5 to 30 ft. When the solids mixture enters the curved section 3B at the indicated velocities, it is subjected to anA ap preciablecentrifugal force which causes the heavier particles to concentrate toward the outside of the curve and the. lighterparticles toward.-

' of solids supplied to reoxidizer 50.

balance the heat produced in the reoxidizer with the inside of the curve. The mass leaves curve 30' crudely classied according to density, the

bottom layer of the contents of pipe 32 being enriched in Yrelatively heavy reduced Ametal oxide vand the top layer Vin relatively light reformer catalyst. Depending on the velocity of the -solids this separation may be such as to increase the concentration of reformer catalyst in the uppermost stream.from say 30% to 'I5-80%, ay concentration of 50% being normally adequate"v to maintain the activity of the reformer catalyst to the desired degree. Y

At least a substantial portion of the top layer is removed from pipe 32 by any suitable/means and returned through standpipe 35 provided with control valve 31 to gas -feed line 5 and from there to converter I0. If desired, an aerating or stripping gas such as nitrogen-rich gas from the reoxidizer may be supplied 'to standpipe 35 through line 36. Preferred means for accomplishing the removal of relatively light materials lar to that of converter I0. The suspension of.

solids in oxidizing gas enters reoxidizer 50 through grid i to form thereabove a dense turbulent uidized mass of solids having a well defined upper level 53. The conditions of supercial gas velocity Vand gas throughout are about the same as those specied in connection with converter l0. However, suicient oxygen must be supplied to accomplish the desired reoxidation of the reduced metal oxide, which normally requires about 0.001 to 0.01 lb. of oxygen per 1b. In order to the heat absorbed in the converter, solids must be circulated much faster (possibly 50 times as fas't) as would be necessary based on oxygen transfer requirements alone.

The oxidation reaction in reoxidizer 50 is\ strongly exothermic and the temperature of the solids undergoing reoxidation may be readily maintained at a slightly higher level than the conversion temperature in converter I0, say at about 1500-1900 F., preferably 1600-1800 FJ by a proper control of the oxygen supply or by conventional heat transfer means (not shown). Slightly elevated pressures are favorable for the reoxidation reaction. The reoxidation may rbe run at a somewhat lower pressure than the gas converter by placing the reoxidizer at a high level and having a long standpipe beneath it and above the slide valve which controls the iiow of solids from the reoxidizer. n

Residual oxidizing gas, usually consisting of technically pure nitrogen is withdrawn overhead from reoxidizer 50 through line 55 to be vented or used for any suitable purpose such as for stripping and purging gas, if desired, after the separation and return of entrained solids by conventional means (not shown) Fluidized reoxidized metal oxide containing minor amounts of reformer catalyst is withdrawn downwardly small amounts of a iiuidizing gas supplied through taps 63. Standpipe 60 leads into gas feed pipe 5 wherein the solids are picked up by the hydrocarbon gas feed and returned, together with the solids coming from pipe 35 to converter I0 substantially at the temperature of reoxidizer 50 to supply the heat required for the endothermic reaction in converter l0. Solids of undesirably small particle size and/or spent reformer catalyst may be removed from the system through lines 'l0 and 'l5 and replaced by fresh material added through line I.

It will be understood that my process may be made fully continuous by maintaining a continuous gas feed and withdrawal through pipes 5, 40, I2, and 55 and a continuous circulation of solids through pipes 5, 32, and 35. The relative amounts of solids withdrawn from and returned to converter l0 should be sufficient to maintain the desired reaction temperature in converter lil. In general, a circulation of 5 to 25 lbs. of metal oxide per cu. ft. of hydrocarbon gas to be converted is adequate for this purpose.

Referring now to Figure 2, I have shown therein in greater and enlarged detail preferred means of separating the crudely classified solids in pipe 32 of Figure 1, like reference symbols being used for like parts appearing in both Figures 1 and 2.

The iiuidized solids mixture flowing down through standpipe 20 at a velocity of about 1/2 to 10 it. per second Vwhich may be increased by steam added through line 28 to about 30 to 100 ft. per second is classied by centrifugal force while passing through curved section 30 in such a manner that the concentration of relatively heavy particles increases from the top to the bottom of the solids mixture owing through pipe 32. Standpipe 35 is provided at its upper end with a solids pick-up device 34 which is adjustable in height and penetrates pipe 32 to any desired level. Pick-up device 3ft has a preferably elongated horizontal orice 38 whose length may be about 1/4 to 3A and whose height about le to 1A, of the diameter of pipe 32. By raising or lowering pick-upv device 3G it is possible to remove from pipe 32 fractions of any desired ratio of relatively heavy reduced metal oxide to relatively light reformer catalyst within the limits determined by the concentration gradient across the height of pipe 32. The solids picked up by pick-up `device 34 are passed through standpipe 35 `and gas feed pipe 5 to converter l0, aS described above. Solids by-passing pick-up de- Vice 3d ow through pipe 32 to enter reoxidizer 50 in the manner explained in connection with Figure 1.

I have shown a vertical iiow of the solids mixture through pipe 20 and curved section 30 and invention because the gravitational force may be separating effect ofthe ldirectional change.

However, similar eiTects may be accomplished with a horizontal or inclined direction of flow, provided suiciently high ow velocities and sharp directional changes are chosen. My invention is not limited to a situation wherein the reformer catalyst is specifically lighter than the metal oxide, but it may be readily adapted to a reversed situation, for example wherein the metal oxide is supported on a specically lighter carrier material such as magnesia or alumina and the reformer catalyst is unsupported. In such a case pipe 35 may be connected to line 45 and pipe 32 togline, 5,;,as will he understood by those skilled @in the fart.

` My ,inventionawilli be further illustrated bythe i following specific example Example -Aplant to produce.300,000 s. c.,f./hr. ofsynvthesis gas containing 1.9l parts per volume -ofHz ,per lpart-ofY CO may beoperated-at the conditionsgiven below:

Natural Gas Feed, 100,000S. C. FJHr. Air Feed, 260,000 S. C. F./Hr. Solids circulation Rate Between Vessels l and 50, 750 Tons/Hr.

:Throughput of GaS'Converter, v200 V./V./Hr. SuperlicialGas Velocity in Vessels and 50, 1.0-2.0/Sec.

Catalyst Life, 3 Months.

.- Radius of Curvature of SeparationPipe, it. eSolvids Flow Speed 1n Curve of Separation Pipe, 60 it./sec.

.jDensity of Reformer'Catalyst, C75-1.0 (unfluidized). ,Denstyof Redueible Oxide, 2.5-4.0 (unfluidized). yParticle Sizes, about through/325 mesh and all liner than 100 mesh.

Reference is made tomy copending application VSerial vNumber 679,885, filed June 2B, 1946, now abandoned, forimprovement in Solids Separation, wherein meansfor separating finely divided solids of different specific gravity,.appli cable in my present invention, are disclosedY and lclaimed more broadly.

While the foregoing description and' exemplary operations have servedto illustrate speciiic ap `plications and vresults of the invention, other -modications obvious to those .skilledinthe art are within the scope of the invention. Onlysuch `limitations should be imposed on thev invention as are indicated in the appended claims.

I claim:

1. Themethod of converting normally gaseous hydrocarbonsiby oxidation and reformatoninto gas mixtures containing carbon monoxide and hydrogen which comprises maintaningfin a conversion zone .a mixture of finely divided vmetal oxide and metallic nickel-containing lreformer catalyst having a particle weightdierent from that of said metal oxide, said' mixture `being uidized by a gas yto form a dense turbulent Isolids phase resembling a'boiling liquid, contactving a normally gaseous -hydrocarbon at conversion conditions with said solids phase, withdrawing a `portion of said mixture from said conversion zone,

passing said portion through a confined. path'involving a directional changelat a-Velocityl suiiciently highto create an'appreciable Acentrifugal iforce at' the point of directional change, the 'direction of said path directly preceding said direc- "60 tional change being substantially vertically downward andthe direction of saidpath directly sub- .sequent tov said directionalchange:being substantiallyfhorizontal,- separatnga fractionrrelatively fgenriched in metal oxide from afraction relatively enriched in reformercatalyst. ata Ypoint -onsaid path subsequent to .said ,directional change, `sub- ."/5 Vjectingv said rst named fraction to oxidizing con- Vditions in an oxidizinggzone, and returning said second named fraction andv` said iirst named oxidized fraction Vto said conversion zone.

.2. The method-of claim 1 wherein said metal l0 oxide is present in a form having a partclewei-ght less than that of'said reformer catalyst.

3. The method of claiml-.w-hereinsaid reformer catalyst is present in a `form having'a particle weight less than that of said metal oxide.

4.The method of claim 3 wherein said reformer catalystA comprises 'nickel' supported on a carrier having a density lesslthan' that of said nickel.

5. The method :of converting normally gaseous "hydrocarbons by oxidation and reformationfinto 20-gas mixturesV containing carbon monoxide and hydrogen which comprises maintaining in aconversion zone a mixture of finely divided metal oxide and Vnickel-containing reformer catalyst 'having a particleI weight'diierentfrom that of 1.25 .said metal oxide, said mixture being uidized by a gas to Aform a dense turbulent solids phase resembling. a boiling liquid, contacting a normally gaseous -hydrocarbon at conversion conditions with said solids phase, withdrawing aportion of 30 said mixture downwardly'from said Aconversion zone, passingV said mixture asa dense .,aerated mass or solids in substantially verticalfdownward v'now through a ccniined path ofsulhcient Ylength vto lbuild up a substantial pseudo-hydrostatic .-1,35 pressure on the `baseof said path, suddenly lchanging the direction of solids flow-adjacent to said base tobecome-,substantially non-.vertical in -acontinuation of said path at 'a-velocitysuiil ciently high to` create an appreciable centrifugal 11140 lforce at the direction of.` said change, separating a fraction relatively enriched in metal oxide from fraction-relatively enriched'in reformer catalyst atl a point l within' said continuation, subjecting .saidrst named fraction to oxidizing conditions in an oxidizing zoneyand returning saidv second `named-fraction and saidvoxidized first named -fraction to said conversion zone.

ALBERT B. WELTY,.JR.

.REFERENCES CITED 4The following references are of record in the file ofY this patent:

UNITED STATES'PATENTS Number Name Date 2,022,778 Maier l Dec..3, 1935 2,039,603 Maier May 5,1936 2,044,915 Mosley June 23, 1936 2,398,954 .Odell Apr. 23, 1943 v2,425,754: Murphree et al. Aug. 19, 1947 2,443,673 Atwell rJune..22, .19.48 2,462,891 Noll Mar. 1, v1.9.49 

1. THE METHOD OF CONVERTING NORMALLY GASEOUS HYDROCARBONS BY OXIDATION AND REFORMATION INTO GAS MIXTURES CONTAINING CARBON MONOXIDE AND HYDROGEN WHICH COMPRISES MAINTAINING IN A CONVERSION ZONE A MIXTURE OF FINELY DIVIDED METAL OXIDE AND METALLIC NICKEL-CONTAINING REFORMER CATALYST HAVING A PARTICLE WEIGHT DIFFERENT FROM THAT OF SAID METAL OXIDE, SAID MIXTURE BEING FLUIDIZED BY A GAS TO FORM A DENSE TURBULENT SOLIDS PHASE RESEMBLING A BOILING LIQUID, CONTACTING A NORMALLY GASEOUS HYDROCARBON AT CONVERSION CONDITIONS WITH SAID SOLIDS PHASE, WITHDRAWING A PORTION OF SAID MIXTURE FROM SAID CONVERSION ZONE, PASSING SAID PORTION THROUGH A CONFINED PATH INVOLVING A DIRECTIONAL CHANGE AT A VELOCITY SUFFICIENTLY HIGH TO CREATE AN APPRECIABLE CENTRIFUGAL FORCE AT THE POINT OF DIRECTIONAL CHANGE, THE DIRECTION OF SAID PATH DIRECTLY PRECEDING SAID DIRECTIONAL CHANGE BEING SUBSTANTIALLY VERTICALLY DOWNWARD AND THE DIRECTIONAL OF SAID PATH DIRECTLY SUBSEQUENT TO SAID DIRECTIONAL CHANGEK BEING SUBSTANTIALLY HORIZONTAL, SEPARATING A FRACTION RELATIVELY ENRICHED IN METAL OXIDE FROM A FRACTION RELATIVELY ENRICHED IN REFORMER CATALYST AT A POINT ON SAID PATH SUBSEQUENT TO SAID DIRECTIONAL CHANGE, SUBJECTING SAID FIRST NAMED FRACTION TO OXIDIZING CONDITIONS IN AN OXIDIZING ZONE, AND RETURNING SAID SECOND NAMED FRACTION AND SAID FIRST NAMED OXIDIZED FRACTION TO SAID CONVERSION ZONE. 